My 15month old screams and cries when i put her in her bed at night,but sleeps fine during day?afraid of dark?

ive tried lullaby cd's and stories etc but as soon as i leave she jumps up and screams and cries for me? Please any help? I cant let her cry its just unfair and i hate her being so upset. Shes such a fanastic bright little girl, she started walking at 10months and now she can say lots of words and can do the most amazing things, she is very bright and advanced for her age so i dont understand why shes so scared and upset at night times? She loves her room and her new bed, going down fully awake for her nap is fine, no fuss at al. So im thinking maybe its something to do with the light situation, should i get her a nightlight pal? Thanks